So That's Why

Your body can make Vitamin D from sunlight — so why is nearly half the global population still deficient in it?

In this episode of So That's Why, Jen, Chris, and Matt unpack what Vitamin D is actually doing inside the body, why the sunshine route fails so many people, and why deficiency shows up as fatigue, frequent illness, and muscle weakness rather than just weak bones. Along the way, they bust the sunscreen myth, explain why D3 is not the same as D2, and make the case for why Vitamin D supplementation is one of the most cost-effective health decisions available.

Timestamps 00:00 — Introduction 02:14 — Why Vitamin D is also classified as a hormone 05:18 — How the body produces Vitamin D from sunlight 06:07 — Why so many people are deficient despite sunshine 09:32 — Food sources, fortification, and supplementation 11:03 — How much Vitamin D do you actually need? 14:46 — The bigger picture: sleep, immunity, and muscle function

Vitamin D Is a Hormone as Much as a Vitamin

[02:14]

Most people know Vitamin D as a bone health supplement. What fewer people know is that it functions as a hormone — one that regulates over a thousand genes and has receptors in virtually every cell in the body.

"Vitamin D regulates over a thousand genes. It coordinates calcium absorption, it manages immune function, it helps maintain muscle strength and influences cellular processes throughout your body." — Jen

This is why deficiency produces such a varied range of symptoms. It is not one system failing — it is the body's master regulator running below capacity.

Why Sunlight Alone Is Not Enough

[06:07]

The UV radiation needed to produce Vitamin D requires sunlight at the right angle — typically midday sun. Anyone living above around 35 degrees latitude, roughly north of Los Angeles or Southern Spain, cannot produce Vitamin D from winter sunlight at all. For UK listeners specifically, Chris shares a striking statistic: if you live north of Milton Keynes, the average year does not deliver enough UV to consistently maintain Vitamin D production.

But latitude is only part of the picture. The Middle East records a 65% deficiency rate despite abundant sunshine, because staying indoors or covering up to escape heat means the skin never gets adequate exposure. Parts of Australia and some areas of India show similarly high rates. Skin pigmentation matters too — melanin reduces Vitamin D synthesis, meaning people with darker skin need significantly more sun exposure to produce the same amount. As Jen points out, darker skin in a northern climate is a genuine double challenge and a health equity issue that deserves more attention.

"If you live north of Milton Keynes, on the average year, you don't get enough UV for the entirety of the year to consistently produce Vitamin D." — Chris

On sunscreen: Chris is unequivocal — the idea that sunscreen blocks Vitamin D production is a myth. Sunscreens reduce UVB rays but not completely; enough UV still gets through for Vitamin D synthesis. Please do not avoid sunscreen for the sake of Vitamin D.

What Deficiency Actually Does to the Body

[02:23]

The effects of Vitamin D deficiency extend well beyond bone health.

1. Calcium absorption: Without adequate Vitamin D, the body absorbs only around half the dietary calcium it should. Bones do not mineralise properly — structurally present but soft and weak.
2. Immune function: Vitamin D controls antimicrobial peptides — the first line of defence against bacteria and viruses — while simultaneously preventing the immune system from overreacting and attacking the body's own tissues. As Jen puts it: it is about balance, not just strength. This is why deficiency links to both increased infection risk and increased autoimmune disease risk.
3. Muscle strength: Deficiency causes proximal muscle weakness — the large muscles in the thighs and upper arms — affecting everyday activities like stair climbing and standing from a chair. Chris notes this happens regardless of training level.
4. Sleep quality: Vitamin D receptors exist in the brain regions that regulate sleep-wake cycles. Deficiency links to poor sleep quality, difficulty falling asleep, and reduced deep sleep.

"There are multiple systems running below capacity — and understanding the why helps prioritise it." — Matt
D3 vs D2 — Why the Form Matters

[09:32]

Food sources of Vitamin D are limited and unreliable. For most people, supplementation is the most practical and consistent option. When choosing a supplement or fortified food, the form matters: Vitamin D3 is nearly 90% more effective than Vitamin D2, and is the form the body naturally produces from sunlight. Many fortified foods use D2 as a default, often labelled as the vegetarian option — but plant-source D3 is now available, and as Chris confirms, is directly equivalent to animal-derived D3. The body cannot tell the difference.

The European safe upper limit for ongoing daily intake is 4,000 IU per day.

"Consistency beats perfection — daily supplement, weekly high dose, or fortified foods plus supplementation. Whatever you'll actually stick to." — Jen
About So That's Why

So That's Why is a weekly podcast where Jen, Chris, and Matt unpack the science behind everyday health questions. No jargon, no judgment — just genuine curiosity and proper research.

Cholesterol is in every single cell in your body — yet it's also called "the Silent Killer." In this episode, Jen, Chris and Matt unpack why the same molecule that keeps you alive can silently damage your arteries for decades before you feel a thing, and what you can actually do about it.

In this episode: 00:00 — Introduction 01:02 — Why cholesterol has such a confusing reputation 02:09 — The scale of the risk: what elevated LDL actually does 04:13 — LDL vs HDL: how cholesterol travels through your body 05:34 — How arterial plaque forms (and why it takes decades) 07:05 — Why boosting HDL isn't the simple fix it seems 08:27 — Age, genetics and why cholesterol tends to creep up 10:41 — Diet, fibre and the practical changes that work 12:25 — Exercise, statins and how quickly they take effect 13:48 — How cholesterol connects to sleep, weight and diabetes 15:34 — So that's why we need to manage our cholesterol levels

Key PointsCholesterol Isn't the Enemy — Excess LDL Is

Timestamp: 04:13

Cholesterol is a single molecule that your body uses to build cell membranes, produce hormones and even synthesise vitamin D. Because it's fat-soluble, it can't travel through your bloodstream on its own — so your body packages it into transport vehicles called lipoproteins.

LDL (low-density lipoprotein) delivers cholesterol from the liver to cells around the body. In normal amounts, this is healthy and necessary. The problem starts when there's too much circulating. HDL (high-density lipoprotein) works in the opposite direction, collecting excess cholesterol from tissues and returning it to the liver for excretion.

"When everything's working normally, LDL is doing its job in a normal and healthy way. The problem is when you've got too much LDL cholesterol circulating." — Chris
What Actually Happens Inside Your Arteries

Timestamp: 05:34

When excess LDL infiltrates an artery wall, the immune system sends in white blood cells to clean it up. But those white blood cells get overwhelmed. They keep consuming damaged LDL particles until they're completely stuffed, transforming into what are known as foam cells.

These foam cells trigger inflammation and attract more white blood cells, creating a vicious cycle. The result is arterial plaque — a fatty deposit that builds up inside the artery wall. As it grows, blood clots can form. A clot in a heart artery causes a heart attack. A clot in a brain artery causes a stroke. The whole process can unfold silently over decades.

"Foam cells sound like something you'd find in a posh latte. It's probably not as pleasant when they're accumulating in your arteries." — Jen
80% of Your Cholesterol Comes From Your Liver, Not Your Diet

Timestamp: 07:53

Most people assume cholesterol is primarily a dietary problem. In reality, around 80% of your cholesterol is produced by your own liver, with only 20% coming from food. This is why some people can eat well and exercise regularly and still have elevated LDL — genetics play a significant role.

For those with familial hypercholesterolaemia (FH), an inherited condition affecting approximately one in 200 people, LDL levels are two to three times higher than normal from birth. Without treatment, around 50% of men with FH develop heart disease before the age of 50. It's typically managed with statins from childhood.

"Risk assessment looks at the whole picture. The same cholesterol number carries very different implications depending on context." — Chris
The Good News: Cholesterol Is Highly Manageable

Timestamp: 10:41

Cholesterol is one of the most manageable risk factors in medicine. For many people, lifestyle changes alone can reduce LDL by 20 to 30%. Statins can reduce it by up to 60%. Diet and exercise changes show results within four to eight weeks; statins work within around six weeks.

Key practical steps include reducing saturated fat (red meat, full-fat dairy), replacing it with healthy fats like olive oil and omega-3 rich foods, increasing soluble fibre from oats, beans, lentils and fruit, and aiming for at least 150 minutes of moderate exercise per week. Getting a simple blood test is the essential first step — because without symptoms, it's the only way to know where you stand.

"For most people, lifestyle change alone can reduce LDL cholesterol by 20 to 30%. And taking statins can reduce it by up to 60%." — Chris
About So That's Why

So That's Why is a weekly podcast where Jen, Chris and Matt unpack the science behind everyday health questions. No jargon, no judgment — just genuine curiosity and proper research.

That irritable, short-fused feeling when you've missed a meal has a name — and it turns out "hangry" is backed by serious science, not just a lack of willpower.

In this episode, Jen and Chris are joined by Jamie for a deep dive into why hunger hijacks your mood. The team unpacks four separate biological mechanisms that fire simultaneously when blood sugar drops: stress hormones that can't be distinguished from a genuine threat, a brain molecule that links hunger and aggression through the same neural circuits, a shutdown of the brain's impulse filter, and a drop in serotonin. Then there's a psychological layer on top — and understanding it might be the most practically useful thing you take away from this episode.

Timestamps

00:00 - Introduction: Jamie joins the show 02:16 - How big a deal is hanger? The 21-day study 03:37 - Blood sugar and why your brain panics 04:06 - Why hunger and stress feel chemically identical 05:05 - Neuropeptide Y: hunger and aggression on the same circuit 06:00 - The prefrontal cortex goes offline 06:39 - Serotonin and the fourth mechanism 07:14 - The psychology of hanger: why you blame the wrong thing 09:35 - What actually helps 11:35 - Hanger, sleep, and gut health 13:03 - So that's why we get hangry

Hunger Accounts for More Than a Third of Your Irritability

The first large-scale study to track hanger in real everyday life followed 64 participants over 21 days. Five times a day, they recorded their hunger levels and emotions via smartphone. The results: hunger accounted for 37% of the variation in irritability and 34% of the variation in anger levels — even after controlling for age, sex, BMI, and personality traits.

"More than a third of the time someone's being irritable, they might just need a sandwich. That reframes a lot of workplace disagreements." — JamieYour Body Can't Tell the Difference Between No Food and a Bear

When blood sugar drops, the body releases cortisol and adrenaline to mobilise glucose. The problem? Cortisol and adrenaline are also the hormones released under stress. The chemical signal for "I need food" and the signal for "I am under threat" are virtually identical. Research confirmed this by temporarily blocking the brain's ability to use glucose — cortisol rose and stress responses emerged, driven through the brain's stress pathways rather than by physical energy depletion alone.

"So my body literally can't tell the difference between there's no food and there's a bear. That seems like a design flaw." — JamieHunger and Aggression Run on the Same Brain Wiring

Neuropeptide Y (NPY) is one of the brain's most potent appetite-stimulating molecules. But the same NPY pathways that drive hunger also increase aggression, because they operate through shared circuits with serotonin. A study confirmed that NPY released during food deprivation directly reduces activity in brain regions that normally suppress aggression.

"Hunger and anger are literally using the same wiring in the brain. That's like having your heating and your smoke alarm on the same circuit — turn one on and the other starts going off." — JamieThe Psychology Layer: Why You Blame the Wrong Thing

A series of experiments showed that hunger alone isn't enough to trigger hanger — it requires biology, environment, and self-awareness working together. Hungry participants only interpreted situations negatively when already exposed to negative cues. In neutral environments, hunger didn't trigger hanger. Critically, participants who reflected on their emotions beforehand didn't become hangry even in deliberately frustrating situations — showing that recognising hunger as the source of irritability can short-circuit the whole process.

"Hanger is basically a case of mistaken identity." — Jamie
About So That's Why

So That's Why is a weekly podcast where Jen, Chris, and the team unpack the science behind everyday health questions. No jargon, no judgment — just genuine curiosity and proper research.

Why do onions make us cry every time we cut them — and why does cooking them make the problem disappear completely?

About 70% of people experience significant tearing when cutting onions, and no matter how many you've chopped over the years, the reaction doesn't get easier. In this episode, Jen, Chris, and Matt unpack the full chemistry behind one of cooking's most universal frustrations. They explore the two-enzyme system inside every onion, the volatile compound it produces, the sulfuric acid that forms on your cornea, and why some people are hit far harder than others. They also look at what actually reduces the reaction — and what the so-called folk remedies get wrong.

Timestamps

00:00 Introduction 01:42 The Two-Enzyme System Inside Every Onion 03:25 The Second Enzyme Discovered in 2002 05:58 Sulfuric Acid and the Wasabi Receptor 07:55 Why Some People React More Than Others 10:09 What Actually Works to Reduce Tears 12:04 Why Garlic Doesn't Make You Cry

The Science of Onion TearsThe Two Chemicals Inside Every Onion That Only React When You Cut It

Timestamp: 01:42

Every onion stores two chemical components in completely separate cellular compartments, physically prevented from interacting. One compartment holds an enzyme called alliinase; the other holds reactive substances called amino acid sulfoxides. As Jen explains, it's like storing oxidiser and fuel in separate tanks — perfectly stable when apart, but the moment a knife ruptures those cell walls, the compartments break open and the reaction begins. Alliinase reacts with the sulfoxides to produce unstable compounds called sulfenic acids, and from there, a second enzyme takes over.

The Enzyme Nobody Knew About Until 2002

Timestamp: 03:25

For most of human history, nobody could fully explain why onions make us cry. In 2002, Japanese researchers finally identified the missing piece: a second enzyme called lachrymatory factor synthase (LFS). This enzyme intercepts the sulfenic acids produced in the first reaction and converts them into a volatile compound — syn-propanethial-S-oxide — that immediately becomes airborne. High-speed camera studies have clocked the tiny droplets ejected from a cut onion at speeds of up to 40 metres per second, roughly 89 miles per hour. The entire two-step reaction completes within seconds of your knife making contact. This is also why sharper knives genuinely help: cleaner cuts rupture fewer cell walls, producing fewer droplets at lower velocity.

"The stats are enough to make you cry." — ChrisSulfuric Acid, the Wasabi Receptor, and Why You Can't Build a Tolerance

Timestamp: 05:58

When those airborne droplets reach the eye, the volatile compound dissolves into the moisture on the surface of the cornea and reacts to form dilute sulfuric acid. The cornea is densely packed with nerve endings designed to detect harmful chemicals, and tears are the body's immediate safety response. The specific receptor triggered is TRPA1, better known as the wasabi receptor, because it responds to the same class of pungent compounds found in mustard, horseradish, wasabi, and onions. When sulfuric acid activates this receptor, a signal travels along the nerves to the brainstem, which fires the tear response — all within milliseconds of the compound arriving.

Crucially, this receptor doesn't adapt. Reaction intensity has no correlation with cooking experience. Every cut into a raw onion triggers the same chemical sequence, every time.

Why Some People React Far More Strongly Than Others

Timestamp: 07:55

The same onion can leave one person unaffected while reducing another to tears. Two factors drive the variation: the onion itself, and individual biology. Different onion varieties produce vastly different enzyme concentrations — there can be up to a threefold difference even within a single variety. Beyond that, people vary in their corneal receptor sensitivity, their baseline rate of tear production, and how efficiently their eyes flush out the irritant. None of these factors are within our control, and none change with repeated exposure.

"I have to time my meal prep to when the family aren't around. Otherwise they're just gonna laugh at me the whole time." — Matt
About So That's Why

So That's Why is a weekly podcast where Jen, Chris, and Matt unpack the science behind everyday health questions. No jargon, no judgment — just genuine curiosity and proper research.

Brain fog affects over a quarter of us — yet it isn't actually a medical diagnosis. So what's really happening inside your brain when thinking feels like wading through treacle?

In this episode, Jen, Chris, and Matt unpack the real biological mechanisms behind brain fog — from neuroinflammation and a compromised blood-brain barrier to mitochondrial dysfunction and hormonal shifts. The team explains why your brain's immune cells can get stuck in "emergency mode," how chronic stress physically shrinks the part of your brain responsible for memory, and why up to 95% of serotonin is produced in your gut, not your brain. Most importantly, they explain why brain fog is typically reversible once you address what's causing it.

In this episode:

1. 00:00 — Introduction and what brain fog actually is
2. 01:38 — Your brain's energy demands and neuroinflammation
3. 03:24 — The blood-brain barrier and why it leaks
4. 05:35 — Mitochondria and the vicious cycle
5. 07:04 — Sleep and the brain's rubbish collection
6. 08:15 — How chronic stress shrinks your hippocampus
7. 09:34 — Hormones, menopause, and thyroid
8. 11:30 — Dehydration, gut health, and nutritional deficiencies
9. 14:30 — What you can actually do about brain fog
10. 17:33 — Why everything is connected
11. 19:01 — So that's why we get brain fog

Your Brain's Immune Cells Can Get Stuck in Emergency Mode

(01:38)

One of the major drivers of brain fog is neuroinflammation — when the brain's immune cells, called microglia, become activated and stay activated long after the initial threat has passed. These cells keep releasing inflammatory molecules called cytokines, which disrupt normal brain signalling.

"Studies using brain imaging found that patients with post-COVID brain fog show widespread microglia activation — their brain's immune cells are basically still in this emergency mode, months after the infection." — Chris

The degree of inflammation directly correlates with symptom severity — the more inflamed the brain tissue, the worse the cognitive symptoms. Those cytokines impair memory, attention, and mental clarity.

This connects to the blood-brain barrier — the membrane that controls what enters the brain from the bloodstream. A 2024 study found that in long COVID patients with brain fog, this barrier becomes compromised, allowing inflammatory molecules and cells that should never reach the brain tissue to get in.

"The security gate isn't just ajar — it's actually letting through some suspicious characters that really shouldn't be getting in." — Matt

The barrier disruption was most notable in the temporal lobes and frontal cortex — regions crucial for memory and attention.

Sleep Deprivation Cancels Your Brain's Rubbish Collection

(07:04)

Sleep sits at the top of the brain fog trigger list. Research shows that after just one night without sleep, reaction time slows by 50%, working memory drops by 40%, and the ability to form new memories decreases by nearly 40%.

During sleep, the brain goes into maintenance mode — flushing out waste products, including proteins that can contribute to conditions like Alzheimer's. Brain function doesn't typically return to normal until roughly 72 hours after sleep deprivation.

"Pulling an all-nighter essentially cancels the brain's rubbish collection." — Matt

Chronic stress compounds the problem. Cortisol — the body's main stress hormone — can physically shrink the hippocampus when it stays elevated for too long. Research has shown that people with chronically high cortisol levels often have a smaller hippocampus and perform worse on memory tasks. And because the hippocampus also helps regulate stress, damage to it means the brain can't keep cortisol in check — creating a vicious cycle.

Hormones, Gut Health, and the Triggers Most People Overlook

(09:34)

Oestrogen acts as a neuroprotective hormone in the brain — supporting memory, enhancing blood flow, and protecting cells from damage. During perimenopause and menopause, when oestrogen levels drop, many women experience brain fog for the first time. Studies have documented measurable cognitive changes during these transitions.

"Women aren't just being emotional or stressed. Their brains are actually responding to dramatic shifts in a hormone that's been protecting and supporting their cognitive function for decades." — Jen

Thyroid hormones are equally important. Nearly 80% of people with hypothyroidism report frequent brain fog symptoms — the direct result of brain cells operating at a slowed metabolic rate.

The gut-brain connection adds another layer. The brain and gut communicate bidirectionally through the gut-brain axis, and up to 95% of serotonin — crucial for mood and cognition — is produced in the digestive system. Studies have shown that patients with irritable bowel syndrome often experience brain fog, and treatments that help rebalance the gut microbiome can improve cognitive symptoms.

Brain Fog Is Reversible — Here's What Actually Helps

(14:30)

The encouraging news is that for most people, brain fog is not permanent cognitive decline — it's a reversible state that improves when you address the underlying causes.

1. Sleep — Most adults need seven to nine hours. The brain needs that time for maintenance, waste clearance, and memory consolidation.
2. Hydration — The brain is over 70% water. Even mild dehydration impairs cognitive function, but effects reverse quickly once you rehydrate.
3. Nutrition — Omega-3 fatty acids, B vitamins, vitamin D, and natural antioxidants all support cognitive function. Limiting processed foods that trigger inflammation is also worth considering.
4. Stress management — Chronic stress physically damages the hippocampus. Finding what works for you — mindfulness, breathing exercises, walking outside — helps break the cortisol cycle.
5. Exercise — Physical activity increases cerebral blood flow, supports mitochondrial function, reduces inflammation, and regulates stress hormones.

"Brain fog's telling you that something needs attention. But your brain is incredibly resilient. If you address the underlying cause, give it the support, your cognitive function typically does improve." — Jen

For brain fog that coincides with perimenopause, menopause, or thyroid issues, speaking with a doctor is recommended — there are treatments that can help.

About So That's Why

So That's Why is a weekly podcast where Jen, Chris, and Matt unpack the science behind everyday health questions. No jargon, no judgment — just genuine curiosity and proper research.

The ingredients on your supplement label that aren't the vitamin? They're not "fillers" and they're not there to cut corners. Most people don't know what these extra ingredients actually do, or why they're necessary.

In this episode, Jen, Chris, and Matt tackle one of the most debated topics in the supplement world. With Chris's 30+ years as a formulation scientist, the team explains why supplements physically cannot be made from pure nutrients alone, what common excipients actually do, and where the real concerns in this industry lie. Along the way, they bust myths about magnesium stearate, silicon dioxide, maltodextrin, and carrageenan, and reveal some genuinely questionable practices hiding behind "filler-free" marketing.

In this episode:

1. 00:00 - Introduction
2. 01:32 - Why supplements can't just be pure nutrients
3. 04:01 - Magnesium stearate and why it's safe
4. 06:06 - Silicon dioxide and the nanoparticle question
5. 07:57 - Maltodextrin and the dose that makes the poison
6. 10:12 - Carrageenan and research misinterpretation
7. 13:02 - The salt shaker situation
8. 16:42 - What "filler-free" labels actually mean
9. 18:39 - What to actually look for on a label

Why Supplements Can't Be Pure Nutrients

(01:32)

A typical vitamin B12 dose is around 100 micrograms, a millionth of a gram. That's too small to see with the naked eye, let alone measure consistently or form into a tablet. Without excipients, you'd have a pile of powder too tiny and too clumpy to work with.

Chris uses a beach sand analogy to explain the manufacturing challenge. Fine, dry beach sand flows through your fingers almost like liquid and pours easily into a capsule. Wet sandcastle sand? Great for building, but impossible to get through a machine. Most nutrient powders behave like the wet sand. Excipients give them the flow they need.

"Supplement companies don't actually financially benefit by adding these things. These ingredients add cost. So if we could make a tablet with just pure vitamin D3 powder, we would. But the problem is it's often physically impossible." — Chris
The Safety of Common Excipients

(04:01)

The team works through four of the most questioned ingredients on supplement labels.

Magnesium stearate is a salt of stearic acid, a natural fatty acid found in cooking oil, chocolate, and any oily food. It's used in milligram quantities as a flow agent. The FDA considers it safe at up to 2,500 milligrams per kilogram of body weight daily. For an average person, that's 175,000 milligrams. A typical capsule contains around 50 milligrams, or roughly 0.03% of the safety threshold.

"It's kind of ironic, right? Avoiding supplements with magnesium stearate whilst eating everyday foods like chocolate that contain far more of the ingredient seems a bit odd." — Matt

Silicon dioxide (silica) prevents clumping and absorbs moisture. There is a legitimate conversation around nanoparticles, and the European Food Safety Authority has been reviewing this. But most silica used in supplements is non-nano, meaning the particles are larger and raise no safety concerns.

Maltodextrin is derived from starch (potatoes or maize) and serves as a binder and natural sweetener in chewable tablets. Online concerns about its glycaemic index come from studies using many grams per day, compared to the 100–200 milligrams in a supplement tablet. At these levels, maltodextrin does its structural job without any measurable effect on the body.

Carrageenan is a natural gum from seaweed, used to form plant-based soft gel capsules. The inflammation concerns originate from studies on poligeenan, a completely different compound not even permitted for use in foods.

"It's literally like saying water is dangerous because of studies about hydrogen peroxide." — Chris
The Salt Shaker Situation and Hidden Ingredients

(13:02)

The genuinely concerning practices in the supplement industry aren't about which excipients are present. They're about transparency.

Some companies, when their vitamin mix won't flow into capsules, use what Chris describes as "a big salt shaker" full of a flow agent like magnesium stearate, pouring it over the mix at the machine. Because they classify this as a "processing aid," they don't declare it on the label. Some of these companies are simultaneously marketing their products as "filler-free."

The team tested a set of "clean" capsules from another company. The plant extract was beige, but there were visible white specks and white residue in the bottle. Nothing white was listed on the ingredients.

"To forget to list flow aids or sub-ingredients is one thing, but to then be making a big noise about how clean or filler-free the product is, is completely unacceptable." — Chris
What to Actually Look for on a Label

(18:39)

The team offers three things to check when choosing a supplement:

1. Bioavailable forms of active ingredients. Vitamin D3 rather than D2, folate rather than folic acid, EPA and DHA for omega-3, and chelated mineral forms.
2. Full transparency. Every ingredient should be listed, including sub-ingredients and processing aids. If something seems to be missing, ask the company directly.
3. Formulation expertise. Is the company run by formulation scientists, or by marketers importing cheap multivitamins?

"What ultimately matters is whether the product contains the active ingredients that are in the right forms and effective doses, and that the product's been formulated properly." — Chris
About So That's Why

So That's Why is a weekly podcast where Jen, Chris, and Matt unpack the science behind everyday health questions. No jargon, no judgment — just genuine curiosity and proper research.

Most of us have stood next to someone at the gym and wondered: why are they barely glistening while we look like we've run through a sprinkler? The answer is more fascinating than you'd expect — and it completely reframes what heavy sweating actually means.

In this episode, Jen, Chris, and Matt unpack the biology behind sweat rate variation, from the hypothalamus acting as your body's built-in thermostat, to the sweat gland architecture determined by your DNA before you were even born. They explore why fitter people often sweat more (not less), how your body learns to cool itself more efficiently over time, and what you can do to work with your sweat response rather than against it. Chris also walks through a simple method for calculating your personal sweat rate — something most people have never thought to do.

Timestamps 00:00 — Introduction 01:41 — How much sweat rates can actually vary 02:56 — Your brain's built-in thermostat: the hypothalamus 03:51 — Sweat gland architecture, genetics, and the factory analogy 06:42 — Does sweating more mean you're fitter? 08:50 — How to calculate your personal sweat rate 11:57 — How sweat connects to sleep, mood, and energy

The Sweat Rate Gap Is Bigger Than You Think

[01:41]

The variation in how much people sweat isn't small. Chris explains that sweat rates can range from half a litre per hour up to two and a half litres per hour in some athletes — more than a five-fold difference for the same exercise intensity. Beyond the curiosity factor, this has real consequences: research shows that even 2% dehydration caused by sweating can decrease performance by around a fifth, and 40 to 50% of athletes consistently underestimate their sweat losses.

"The variation can mean sweating between half a litre per hour and two and a half litres per hour in some athletes. That's more than a five-fold difference for a similar exercise." — ChrisYour Sweat Glands Work Like Tiny Factories — and Everyone's Are Different

[03:51]

The variation in sweat response comes down to what Chris calls your individual sweat gland architecture. Each gland produces a fluid similar to blood plasma, and then a duct reabsorbs sodium chloride before that fluid reaches the surface of your skin — a built-in quality control process Chris describes as "tiny water treatment plants." Individual differences in how efficiently that reabsorption happens explain differences in both sweat volume and saltiness. Critically, the genes governing sweat gland development are active while we're still embryos, meaning our relationship with sweat is written into our DNA.

"My brain decides how much to sweat without me having any say." — JenFitter People Often Sweat More — Not Less

[06:42]

This section busts one of the most common gym-floor assumptions. People at peak fitness typically begin sweating within one to two minutes of exercise, compared to five or more minutes for less trained individuals. A trained body doesn't wait to overheat — it anticipates the heat and starts cooling proactively. After one to two weeks of regular heat exposure during exercise, the system acclimatises further: heat-acclimatised people produce sweat around six times lower in sodium than unacclimatised people, because the body has learned to conserve its electrolytes.

"Being a heavy sweater can actually be a badge of honour. Which changes everything for people who might feel self-conscious about their sweating." — MattHow to Calculate Your Personal Sweat Rate — and Use It

[08:50]

Chris walks through a simple method: weigh yourself before exercise, exercise for an hour without drinking, then weigh yourself again. The weight difference in kilograms, multiplied by 1,000, gives your sweat rate in millilitres per hour. From there, the team covers practical strategies — including why over-drinking during exercise can deplete electrolyte balance, why timing workouts for the cooler parts of the day can cut sweat losses by 30 to 40%, and why pre-cooling techniques like running cold water over the wrists and forehead are more effective than most people realise.

"There is no universal hydration strategy. It's what's right for you." — ChrisAbout So That's Why

So That's Why is a weekly podcast where Jen, Chris, and Matt unpack the science behind everyday health questions. No jargon, no judgment — just genuine curiosity and proper research.

Think going red during exercise means you're unfit? The science says otherwise. Exercise induced facial flushing has virtually no correlation with fitness level, and it might actually signal a more efficient cooling system.

In this episode, Jen, Chris, and Matt explore why some people turn tomato red during a workout while others barely change colour. The answer lies in genetics, specifically in blood vessel density and reactivity. The team breaks down what's really happening under your skin, why people with pronounced flushing often have better thermal regulation, and what you can actually do about it if it bothers you.

In this episode:

1. 00:00 Introduction
2. 01:04 Why fitness has nothing to do with it
3. 02:47 Blood vessel density and reactivity explained
4. 04:06 Why going red might actually be an advantage
5. 05:39 Ethnicity, gender and age differences
6. 08:09 What actually helps reduce flushing
7. 11:41 The human mood ring connection
8. 13:04 So that's why your face turns red

It's Not About Fitness. It's About Your DNA.

[01:04]

The assumption that you'll stop going red when you get fitter is one of the most persistent myths in exercise culture. Research shows that flushing intensity has virtually no correlation with cardiovascular fitness, effort level, or how out of shape someone is.

As Chris puts it: "It's got virtually nothing to do with fitness level and everything to do with how your cooling system is programmed."

Despite this, the myth has real consequences. Studies have shown that people with pronounced exercise flushing are around 40% more likely to avoid group fitness classes, often choosing to exercise alone or during quieter gym times. That's a significant number of people changing their health routines because of something they can't actually control.

"My fitness has improved loads over the past five years especially, and I still turn bright red." — JenBlood Vessel Density and Reactivity

[02:47]

So what is actually causing the variation? It comes down to two genetically determined factors: blood vessel density and blood vessel reactivity.

1. Blood vessel density refers to the number of blood vessels packed into the skin of the face. This varies greatly from person to person. More vessels near the surface means more visible blood flow when they dilate.
2. Blood vessel reactivity is how quickly those vessels respond to triggers like heat and rising core temperature. Research conducted in Australia found that some people's facial blood vessels react to increases as small as a third of a degree Celsius.

For context, core body temperature during exercise might rise by one to two degrees overall. For highly reactive individuals, their facial blood vessels are already responding before they've barely warmed up.

"In some people it could be responses that kick in when your body temperature increases by just a third of a degree Celsius." — ChrisWhy Going Red Might Be a Superpower

[04:06]

People with high facial vascular reactivity tend to have better overall thermal regulation. Their bodies get ahead of the heat problem before it becomes serious, which means better core temperature maintenance and reduced overheating risk during prolonged activity.

Chris notes that "pronounced facial flushing often correlates with better performance in hot temperatures." Athletes with higher facial vascular reactivity appear to maintain better performance when training in the heat.

The difference comes down to how the body distributes its cooling effort. Some people have distributed thermoregulation, spreading heat dissipation evenly across their body. Others concentrate the response in the face. Same system, same outcome, different display. From a physiological perspective, concentrated facial flushing has no trade offs.

People with this responsive vascular system also tend to blush more easily during emotional stress and react more strongly to spicy foods and temperature changes.

"Those of us who turn red during exercise, basically we're human mood rings." — Matt

The same genetic programming also supports better long term cardiovascular adaptation. People with responsive vascular systems often see resting heart rate and blood pressure reductions faster with training.

"The same genetic programming that's making us look like tomatoes is actually supporting the long-term cardiovascular adaptation." — JenWhat Actually Helps (and What Makes It Worse)

[08:09]

Since flushing is genetic, it can't be eliminated entirely. But the episode covers several evidence backed ways to reduce its intensity:

1. Pre cooling — Applying cool, damp cloths to the wrists and temples for two to three minutes before exercise can reduce facial flushing intensity by about a quarter. These pressure points have blood vessels close to the surface that connect directly to facial capillaries.
2. Hydration timing — A glass of cool water about 20 minutes before exercise helps maintain better temperature regulation. The body needs time to distribute that fluid before heat stress begins.
3. Clothing choices — Light coloured, moisture wicking fabrics reduce overall heat load. The neck area is particularly important, as it contains major blood vessels that supply the face.
4. Avoid alcohol within 24 hours of intense exercise, as it dilates blood vessels and makes flushing more pronounced. Very hot showers immediately after exercise can also prolong the response.

For most people, exercise flushing is completely harmless. If it's accompanied by dizziness, nausea, or confusion, or doesn't resolve within 30 minutes, that's worth checking as it could indicate heat exhaustion.

"It's not a sign of being out of shape. It's a sign that your temperature control system is working exactly as designed." — JenAbout So That's Why

So That's Why is a weekly podcast where Jen, Chris, and Matt unpack the science behind everyday health questions. No jargon, no judgment, just genuine curiosity and proper research.

Think you need to hit 10,000 steps every day? That target didn't come from a doctor or a clinical study. It came from a 1964 Japanese pedometer marketing campaign. In this episode, Jen, Chris, and Matt trace the surprising origin of the world's most famous fitness target and compare it with what modern research actually says about steps and health.

A 2025 study published in The Lancet, analysing data from over 160,000 adults globally, found that the real health benefits of walking kick in much earlier than most people think, and that the ideal step count depends on your age, your health, and your lifestyle.

Key points covered in this episode:

1. 00:00 Introduction
2. 01:43 The huge health benefits of walking
3. 03:19 The 1964 Tokyo Olympics marketing origin
4. 05:10 What researchers actually found decades later
5. 06:38 Why age changes your ideal step count
6. 08:42 Why not all steps are created equal
7. 11:06 What your personal target should be
8. 15:29 Weekend warriors and other forms of exercise
9. 16:28 How steps connect to sleep and mental health
10. 18:21 So that's why we chase 10,000 steps

The 10,000-Step Target Was Born From Marketing, Not Medicine

In 1964, a Japanese company developed one of the first commercial pedometers and named it the Manpo-kei, meaning "10,000 step meter." The number was chosen partly because of its cultural significance in Japan as a symbol of long life, and partly because the Japanese character for 10,000 looks like a person walking.

There was some science in the mix. Dr Yoshiro Hatano at Kyushu University calculated that going from 4,000 to 10,000 steps would burn roughly 500 extra calories per day. But as Jen puts it, "It was basically one guy with a calculator being like, yeah, 10,000 sounds good."

"Our entire fitness culture is based on what a Japanese character looked like. It feels a little bit like deciding to eat eight meals a day because that's the shape of a snowman." — MattThe Science Says You Probably Need Fewer Steps Than You Think

When researchers eventually studied the relationship between step counts and health, they found a more nuanced picture. A major study of 160,000 older women found that just 4,400 steps per day was associated with a 40% reduction in mortality risk compared to 2,000 steps. Benefits plateaued at approximately 7,500 steps.

The Lancet study reinforced this, showing that people walking at least 7,000 steps per day had a 25% reduction in cardiovascular disease risk, 38% lower chance of dementia, and 22% reduction in depression.

The health gains follow a curve that rises steeply at first, then flattens. The biggest improvements come from moving out of a sedentary lifestyle, not from chasing the highest possible number.

"10,000 steps as a daily target's not wrong. It's just not universally right either." — ChrisYour Ideal Step Count Depends on Who You Are

Optimal step counts vary dramatically based on age, health status, height, and lifestyle. For adults under 60, benefits plateau at 8,000 to 10,000 steps. For those over 60, maximum benefits are often reached at 6,000 to 8,000. People with chronic conditions can see meaningful improvements from just 2,000 to 3,000 additional steps per day.

Intensity matters too. A 2024 study found that 15 minutes of brisk walking daily was associated with a nearly 20% decrease in mortality risk. The same number of steps at a slower pace doesn't deliver the same benefit.

"The best exercise you should do is one that you will actually do." — MattSteps Connect to Sleep, Mood, and the Bigger Health Picture

Higher daily step counts are directly linked to better sleep quality, less time falling asleep, and more deep sleep. The mental health connection is equally striking, with a 22% reduction in depression risk at 7,000 steps compared to 2,000.

"Your movement affects your sleep and your sleep affects your mood and that affects your motivation. It all works together." — MattAbout So That's Why

So That's Why is a weekly podcast where Jen, Chris, and Matt unpack the science behind everyday health questions. No jargon, no judgement — just genuine curiosity and proper research.

Less than 1% of the population genuinely needs less sleep. The rest of us claiming to be fine on four or five hours? We're most likely accumulating something called sleep debt, and our brains have become numb to the damage. In this episode, Jen, Chris, and Matt unpack the genetics of natural short sleepers, what your brain actually does while you're asleep, and why "adapting" to less sleep is one of the biggest myths in sleep science.

What You'll Learn

1. Why less than 1% of people carry genuine short-sleep genetics
2. What happens to your brain after just one night of poor sleep
3. The waste-removal system your brain runs every night
4. Why you can't train yourself to need less sleep
5. How age, circadian rhythms, and environment shape your sleep needs
6. Practical ways to figure out what your body actually needs

Key Timestamps

00:00 - Introduction

01:08 - Genetic mutations and natural short sleepers

04:09 - Your brain takes out the trash while you sleep

05:25 - Sleep stages and where the real recovery happens

07:21 - The myth of adapting to less sleep

08:20 - Age, teenagers, and biphasic sleep history

11:33 - Warning signs of chronic sleep debt

13:45 - Circadian rhythms and sleep environment

15:06 - Can supplements help with sleep quality?

16:31 - Why sleep connects to everything else

19:19 - So that's why some people need less sleep

The Genetics of Short Sleep

In 2009, researchers at the University of California, San Francisco, discovered the first family with natural short sleep syndrome. A mother and daughter required just 6.25 hours of sleep per night, compared to 8.06 hours for other family members. The difference was a mutation in the DEC2 gene, which affects the molecular clock in the brain.

As Chris explains: "These people with this ability, this mutation, they don't just cope with less sleep, they actually need less while maintaining the same perfect cognitive function."

Since then, scientists have found other gene mutations with similar effects. But these natural short sleepers remain extraordinarily rare.

"They've won the genetic lottery, except instead of millions, they won the ability to function on less sleep." — MattWhat One Night of Bad Sleep Does to Your Brain

Research involving over 5,000 people found that after just one night of four to six hours of sleep, reaction time slows by 50%, working memory drops by 40%, and the ability to form new memories decreases by roughly 40%.

The unsettling part? People don't realise how impaired they are.

"Your brain adapts to feeling tired, so you think you're functioning normally when you are actually functioning like you've had several drinks." — Jen

That adaptation has a name: sleep debt. And it accumulates quietly.

Your Brain's Nightly Maintenance Routine

During deep sleep, brain cells physically shrink by 60%, opening up space to flush out waste products accumulated during the day, including proteins associated with Alzheimer's disease. An all-nighter essentially cancels this process entirely.

"When someone says they're too busy to sleep, they're saying they're too busy to let their brain take out the trash." — Matt

REM sleep transfers information from temporary storage to permanent storage in the cortex. Miss it, and long-term memory formation suffers.

The Myth of Adapting to Less Sleep

Multiple studies show that while you might feel less tired over time, performance continues to deteriorate beneath the surface.

"It's a bit like altitude sickness. You stop feeling nauseous, but your blood oxygen levels are still dangerously low." — Matt

Warning signs of chronic sleep debt include needing caffeine to function, falling asleep within minutes of lying down, sleeping significantly longer on weekends, and feeling groggy upon waking.

About So That's Why

So That's Why is a weekly podcast where Jen, Chris, and Matt unpack the science behind everyday health questions. No jargon, no judgment, just genuine curiosity and proper research.